1. Field of the Invention
The present invention relates to a lubricant for plastic working. The lubricant is useful as a non-graphite. lubricant in place of graphite lubricants, for the purpose of release during plastic working, i.e. forging, extrusion, rolling, pressing, wire drawing, and other metal working, and particularly hot or warm forging or extrusion.
2. Description of the Prior Art
Lubricants used for plastic working of metal usually consist of oil-dispersed or aqueous-dispersed graphite. The former is prepared by dispersing graphite in a composition of mineral oil mixed with an extreme-pressure agent, wax, or the like, and since most of such working is hot, there exists the risk of ignition and fuming, which are major problems from the standpoint of safety, working environment and health. The latter is prepared by dispersing graphite in water containing an extreme-pressure agent. The lubricity is equal to that of the aforementioned oil dispersions, while there is no problem of ignition and the workability is slightly superior; however, as long as graphite is used there is no change in the blackness pollution to the worker and the working environment, and thus a health issue remains.
Attempts have been made to develop lubricants for plastic working which do not use graphite, in order to overcome these problems in the working environment. Examples thereof include lubricants prepared by adding glass compositions to alkali metal salts of aromatic carboxylic acids (Japanese Unexamined Patent Publication No. 60-1293) and lubricants employing alkali metal salts of phthalic acid .(Japanese Unexamined Patent Publication No. 58-84898). In order to overcome the above-mentioned problems of lubricants, the present applicant has also proposed lubricants employing alkali metal salts of alicyclic hydrocarbon dibasic acids or mixtures of alkali metal salts of such dibasic acids and alkali metal salts of fumaric acid (Japanese Unexamined Patent Publication No. 1-299895); nevertheless, from a practical standpoint their lubricity and releasability are inferior in comparison to graphite lubricants, and this results in disadvantages such as occurrence of product defects, reduction in workability and reduction in mold life.
Although the conventionally used alkali metal salts of carboxylic acids such as phthalic acid and fumaric acid are effective as heat resistant lubricant components, they differ from colloidal graphite which is a laminar solid lubricant, and lubricants under extreme pressure have low dispersability and are prone to film cracking between the mold and the worked product during the plastic working. As a result, the lubrication of the mold is reduced, sticking occurs, and abrasiveness of the mold is increased.